In the area of user resource allocation for wireless fading channels, great effort is presently focused on scheduling [1-2]. Scheduling algorithms can typically be classified into channel-dependent or channel-independent scheduling according to the dependence on the channel. An example of such an algorithm is Round Robin (RR), a typical channel-independent scheduling, which benefits from simplicity at the price of poor performance. The class of channel-dependent scheduling algorithms utilize the so-called channel state information (CSI) or channel quality indicator (CQI) in order to improve the system performance.
For OFDM systems, the above mentioned channel-dependent scheduling can be further classified into so called time-domain scheduling, where a single user or user terminal per frame is scheduled in a given time scale, and so called time-and-frequency-domain scheduling, where multiple users per frame are scheduled exclusively in a given time scale. The time-and-frequency-domain scheduling, hereinafter referred to as frequency-domain scheduling, has previously been shown to provide better performance than the time-domain scheduling due to the multi-user diversity in the frequency domain, especially for wideband transmissions [1]. However, the frequency-domain scheduling requires CSI or CQI feedback once per frequency-domain resource unit, which requires extensive overhead signaling that is much higher than that for time-domain scheduling, i.e. one feedback for the whole band at a time. In addition, there are many different detailed criteria for the frequency-domain scheduling, such as Max-CIR, Proportional-Fair (PF), weighted-queue-PF etc [3], for both frequency-domain and time-domain scheduling.
For the class of channel-dependent scheduling algorithms the time-domain scheduling has the advantages of low computational complexity and low signaling overhead (for it self and power allocation, link adaptation afterwards as well). However, due to the frequency-selectivity along the wideband, the time-domain scheduling cannot guarantee that the scheduled user performs well on the whole band, therefore, can hardly achieve good performances in capacity and coverage.
Frequency-domain scheduling schemes perform the criteria in the more refined sub-group (e.g. chunk) of the whole band, and utilize the multi-user diversity as well, so that the performances in capacity and coverage are greatly improved as compared to the time-domain scheduling schemes.
However, the disadvantages of the otherwise advantageous frequency-domain scheduling increase as the performance improves. Specifically, the computational complexity increases greatly with the number of chunks and the system load. In addition, since the scheduled user terminals may be different from one chunk to another, a large quantity of DL signaling is required for the frequency-domain adaptation (FDA), including the chunk allocation and the subsequent power allocation and link adaptation per user. The signaling overhead thus increases linearly with the increasing bandwidth, i.e. with the number of chunks, and with the system load, i.e. the number of users.
These disadvantages have prevented, up until now, the further exploitation of channel-dependent time-and-frequency domain scheduling.
Consequently, there is a need for methods and arrangements enabling exploiting the advantages of channel-dependent time- and frequency domain scheduling whilst at the same time reducing the known disadvantages.